A denial of service vulnerability exists in the Exif module of PHP. The vulnerability is due to a null pointer dereference in exif_process_user_comment when trying to handle JIS encoded user comment Exif tags when multi-byte string support is enabled in PHP. A remote, unauthenticated attacker can exploit this vulnerability by having the target PHP application process Exif data on a maliciously crafted image. Successful exploitation would cause the PHP interpreter to crash, leading to a denial of service condition.